Digital-to-analog converters are used in many electronic devices providing an electrical output signal or a physical non-electrical output signal. Such devices include e.g. electronic digital devices having antennas for transmitting electromagnetic waves or for providing audible signals such as mobile telephones and CD players. A DAC receives at periodically repeated times an input digital signal and provides at times somewhat after said repeated times an output signal, such as an electric voltage or current, having a magnitude that should be proportional to a value that the previous input signal represents. The time period between said periodically repeated times has a length called the updating period time.
Besides e.g. component mismatch, an important limiting factor affecting the linearity of current-steering DACs is the nonideal behavior of current sources and switches due to parasitic resistances and capacitances. This problem has been discussed in J. J. Wikner and N. Tan, “Modeling of CMOS digital-to-analog converters for telecommunication”, IEEE Trans. on Circuits and Systems II, Vol. 46, No. 5, pp. 489-499, May 1999, A. van den Bosch, M. Steyaert, and W. Sansen, “SFDR-bandwidth limitations for high speed high resolution current steering CMOS D/A converters”, Proc. 6th IEEE Int. Conf. on Electronics, Circuits, and Systems, Vol. 3, 1999, pp.1193-1196, J. J. Wikner and N. Tan, “Influence of Circuit Imperfections on the Dynamic Performance of DACs”, NorChip'97 Conference, Tallinn, Estonia, November 1997, K. O. Andersson and J. J. Wikner, “Characterization of a CMOS current-steering DAC using state-space models”, Proc. IEEE 2000 Midwest Symposium on Circuits and Systems, MWSCAS'00, Lansing, Mich., USA, August 2000, J. J. Wikner, “Studies on CMOS Digital-to-Analog Converters”, Linkoping Studies in Science and Technology, Dissertation No. 667, ISBN 91-7219-910-5, 2001, and M. Gustavsson, J. J. Wikner, and N. Tan, “CMOS dataconverters for communications”, Kluwer Academic Publishers, 2000.
The influence of the parasitic capacitances at the output nodes of the current sources and current switches is often the most crucial, yielding a dynamic nonlinearity that “grows” with increasing signal frequency, e.g. for a single-tone input signal the third-order harmonic term increases with 15-20 dB/decade of increasing signal frequency, see the three last articles cited above. This normally holds for higher frequencies where the output values of a DAC cannot be approximated by a memory-less expression.